auto update index may cause error

[easypickings]

When I set MSEARCH_ENABLE = True and try to add a new record to the table, it raises error like

Traceback (most recent call last):
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/flask/app.py", line 2463, in __call__
    return self.wsgi_app(environ, start_response)
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/flask/app.py", line 2449, in wsgi_app
    response = self.handle_exception(e)
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/flask/app.py", line 1866, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/flask/_compat.py", line 39, in reraise
    raise value
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/flask/app.py", line 2446, in wsgi_app
    response = self.full_dispatch_request()
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/flask/app.py", line 1951, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/flask/app.py", line 1820, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/flask/_compat.py", line 39, in reraise
    raise value
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/flask/app.py", line 1949, in full_dispatch_request
    rv = self.dispatch_request()
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/flask/app.py", line 1935, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/flask_login/utils.py", line 272, in decorated_view
    return func(*args, **kwargs)
  File "/Users/sucan/compNet/app/routes.py", line 287, in record_add
    db.session.commit()
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/sqlalchemy/orm/scoping.py", line 162, in do
    return getattr(self.registry(), name)(*args, **kwargs)
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 1036, in commit
    self.transaction.commit()
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 510, in commit
    self.session.dispatch.after_commit(self.session)
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/sqlalchemy/event/attr.py", line 322, in __call__
    fn(*args, **kw)
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/flask_sqlalchemy/__init__.py", line 224, in after_commit
    models_committed.send(session.app, changes=list(d.values()))
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/blinker/base.py", line 267, in send
    for receiver in self.receivers_for(sender)]
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/blinker/base.py", line 267, in <listcomp>
    for receiver in self.receivers_for(sender)]
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/flask_msearch/backends.py", line 121, in index_signal
    return self._signal(self, sender, changes)
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/flask_msearch/signal.py", line 42, in default_signal
    backend.create_one_index(instance)
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/flask_msearch/whoosh_backend.py", line 190, in create_one_index
    attrs[field] = str(relation_column(instance, field.split('.')))
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/flask_msearch/backends.py", line 30, in relation_column
    _field = getattr(instance, fields[0])
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/sqlalchemy/orm/attributes.py", line 282, in __get__
    return self.impl.get(instance_state(instance), dict_)
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/sqlalchemy/orm/attributes.py", line 710, in get
    value = self.callable_(state, passive)
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/sqlalchemy/orm/strategies.py", line 747, in _load_for_state
    session, state, primary_key_identity, passive
  File "<string>", line 1, in <lambda>
    
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/sqlalchemy/orm/strategies.py", line 837, in _emit_lazyload
    session.query(self.mapper), primary_key_identity
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/sqlalchemy/ext/baked.py", line 612, in _load_on_pk_identity
    result = list(bq.for_session(self.session).params(**params))
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/sqlalchemy/ext/baked.py", line 444, in __iter__
    return q._execute_and_instances(context)
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/sqlalchemy/orm/query.py", line 3411, in _execute_and_instances
    querycontext, self._connection_from_session, close_with_result=True
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/sqlalchemy/orm/query.py", line 3426, in _get_bind_args
    mapper=self._bind_mapper(), clause=querycontext.statement, **kw
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/sqlalchemy/orm/query.py", line 3404, in _connection_from_session
    conn = self.session.connection(**kw)
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 1133, in connection
    execution_options=execution_options,
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 1139, in _connection_for_bind
    engine, execution_options
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 408, in _connection_for_bind
    self._assert_active()
  File "/Users/sucan/compNet/new_venv/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 276, in _assert_active
    "This session is in 'committed' state; no further "
sqlalchemy.exc.InvalidRequestError: This session is in 'committed' state; no further SQL can be emitted within this transaction.

When set MSEARCH_ENABLE = False, the error disappears. So I guess something with update index may cause error?

[easypickings]

seems mentioned in #24